Propane oxidative dehydrogenation using CO2 over CrOx/Fe–CeO2 catalysts

Abstract

The kinetic behavior of CrO_x sites supported on Fe doped CeO₂ was studied for CO₂-assisted propane oxidative dehydrogenation. The support was synthesized via a co-precipitation method of Fe and Ce precursors while wetness impregnation was used to deposit the CrO_x species. XRD and Raman analysis confirmed the presence of dispersed CrO_x sites on the surface of the support at a low loading while small Cr₂O₃ nanoparticles were found at high loadings. The addition of CrO_x sites reconstructs the available surface oxygen sites and enhances the reducibility of the catalyst as confirmed by H₂-TPR measurements. Herein, we show that the CrO_x based catalysts outperform the parent support at low reaction temperatures both from a propane conversion and propylene selectivity perspective. At elevated temperatures, the effect of CrO_x sites on the propylene production diminishes since propane dry reforming is dominant. A Langmuir–Hinshelwood kinetic model was developed based on 14 elementary steps to account for the dominating reaction pathways, i.e. propane dehydrogenation, reverse water gas shift and dry reforming. The regressed kinetic data showed that the incorporation of CrO_x on the support decreases the activation energy of propane dehydrogenation by 60–75% while a small decrease in the activation energy of dry reforming was noted (∼15%).